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Table 1 Characteristics of study participants; bivariate and full multivariate linear regressionsa, (N = 811)

From: Comparison of subset selection methods in linear regression in the context of health-related quality of life and substance abuse in Russia

Independent variables

n (%)b

Bivariate OLS regression

Full multivariate OLS regression (N = 803)c

Beta

95 % CI

Beta

95 % CI

I. SOCIO-DEMOGRAPHIC CHARACTERISTICS

Sex:

     

 Male

631 (77.8)

Ref

-

Ref

-

 Female

180 (22.2)

1.72

(−0.62 ; 4.06)

−3.25

(−5.61 ; −0.88)

Age (median = 32 y.o):

     

 Less than 32 y.o.

397 (49.0)

Ref

-

Ref

-

 32 y.o. or older

414 (51.0)

−5.21

(−7.27 ; −3.14)

−4.81

(−6.69 ; −2.93)

Education:

     

 Primary or basic

62 (7.6)

Ref

-

Ref

-

 Secondary, vocational or at least some higher

749 (92.4)

7.37

(2.89 ; 11.84)

3.54

(−0.61 ; 7.68)

Main source of income:

     

 Legal source

677 (83.5)

Ref

-

Ref

-

 Illegal source

134 (16.5)

−3.27

(−5.78 ; −0.76)

−0.35

(−2.75 ; 2.05)

Level of income:

     

 Coping well

245 (30.2)

Ref

-

Ref

-

 Coping is difficult (or very difficult)

566 (69.8)

−8.99

(−11.18 ; −6.80)

−3.86

(−6.00 ; −1.73)

Living arrangements:

     

 Someone else’s house

274 (33.8)

Ref

-

Ref

-

 Owned or rented place

512 (63.1)

−3.24

(−5.35 ; −1.13)

1.73

(−0.33 ; 3.79)

 Shelter/no fixed place

25 (3.1)

−5.00

(−10.80 ; 0.81)

0.97

(−4.74 ; 6.69)

Marital status:d

     

 Not married

554 (68.4)

Ref

-

Ref

-

 Married

256 (31.6)

−0.21

(−2.55 ; 2.13)

−0.96

(−3.40 ; 1.49)

II. ALCOHOL AND DRUG USE

Alcohol abuse using CAGE scale:

     

 CAGE = 0–1

274 (33.9)

Ref

-

Ref

-

 CAGE = 2-4

534 (66.1)

−10.10

(−12.20 ; −8.00)

−1.76

(−4.00 ; 0.47)

Age of first drug use (cannabis excluded; median = 16 y.o.):

     

 17 y.o. or older

280 (34.5)

Ref

-

Ref

-

 16 y.o. or younger

531 (65.5)

−6.64

(−8.70 ; −4.58)

−3.38

(−5.47 ; −1.30)

Main drug of use:

     

 (Meth)-amphetamines

27 (3.3)

Ref

-

Ref

-

 Methadone/Fentanyl

221 (27.3)

−6.92

(−11.80 ; −2.04)

1.43

(−3.51 ; 6.37)

 Heroin

563 (69.4)

−14.74

(−19.39 ; −10.08)

0.87

(−4.01 ; 5.74)

Poly-drug use in the last 4 weeks:e

     

 Injected 1 class of drugs

697 (85.9)

Ref

-

Ref

-

 Injected 2 or more classes of drugs

114 (14.1)

−6.15

(−9.08 ; −3.22)

−3.62

(−6.38 ; −0.87)

Frequency of injecting drugs (days during the last 4 weeks; median = 20):

     

 19 days or less

337 (41.6)

Ref

-

Ref

-

 20 days or more

474 (58.4)

−8.37

(−10.49 ; −6.25)

−1.39

(−3.88 ; 1.09)

Frequency of injecting drugs (times per day; median = 1):

     

 One

437 (54.0)

Ref

-

Ref

-

 Two or more

372 (46.0)

−7.69

(−9.79 ; −5.60)

−0.40

(−2.61 ; 1.80)

Used non-sterile injecting equipment at least once in the last 4 weeks:

     

 No (or don’t know)

344 (42.4)

Ref

-

Ref

-

 Yes

467 (57.6)

−10.54

(−12.59 ; −8.50)

−2.05

(−4.41 ; 0.30)

Ever used non-sterile injecting equipment:

     

 No

79 (9.7)

Ref

-

Ref

-

 Yes

732 (90.3)

−10.94

(−14.08 ; −7.81)

−0.55

(−4.13 ; 3.04)

Getting sterile injecting equipment (any unused syringes in last 4 weeks):

     

 No

46 (5.7)

Ref

-

Ref

-

 Yes

765 (94.3)

9.12

(4.77 ; 13.48)

−0.97

(−5.14 ; 3.20)

Ever overdosed:

     

 No

284 (35.0)

Ref

-

Ref

-

 Yes

527 (65.0)

−6.58

(−8.75 ; −4.42)

0.10

(−2.12 ; 2.32)

III. MENTAL HEALTH

Mental health problems score:

     

 Lower score on mental health problems

427 (52.7)

Ref

-

Ref

-

 Higher score on mental health problems

384 (47.3)

−9.27

(−11.28 ; −7.26)

−2.61

(−4.85 ; −0.38)

IV. SEXUAL RISK

Sexually active in the last 6 months:

     

 No

188 (23.2)

Ref

-

Ref

-

 Yes

623 (76.8)

1.75

(−0.73 ; 4.23)

0.91

(−1.69 ; 3.52)

Involved in sexual work in the last 6 months:

     

 No

757 (93.3)

Ref

-

Ref

-

 Yes

54 (6.7)

−0.16

(−3.35 ; 3.03)

2.80

(−1.05 ; 6.66)

Paid for sex in the last 6 months:

     

 No

748 (92.2)

Ref

-

Ref

-

 Yes

63 (7.8)

7.80

(4.65 ; 10.95)

2.25

(−1.11 ; 5.60)

Condom use during the last sexual intercourse:

     

 Yes

378 (46.6)

Ref

-

N/A

-

 No

238 (29.3)

−0.79

(−3.29 ; 1.72)

  

 Don’t know

195 (24.0)

−2.44

(−5.11 ; 0.24)

  

HIV and Hepatitis C status of primary sexual partner:

     

 HIV and HCV negative or unknown

155 (19.1)

Ref

-

Ref

-

 Known to be HIV or HCV positive

218 (26.9)

−11.09

(−14.14 ; −8.04)

−1.98

(−5.05 ; 1.09)

 No primary partner in the last 6 months

438 (54.0)

−8.23

(−11.00 ; −5.47)

−2.02

(−5.04 ; 1.00)

V. INFECTIOUS DISEASES HISTORY AND STATUS

Ever been tested for HIV:

     

 No (or don’t know)

52 (6.4)

Ref

-

Ref

-

 Yes

759 (93.6)

−1.95

(−6.04 ; 2.13)

3.63

(−0.58 ; 7.84)

HIV status awareness:

     

 Result of the most recent HIV test is negative, unknown or never tested

428 (52.8)

Ref

-

N/A

-

 Result of the most recent HIV test is positive

383 (47.2)

−9.71

(−11.74 ; −7.68)

  

HIV status (based on study testing):

     

 Negative

359 (44.3)

Ref

-

Ref

-

 Positive

452 (55.7)

−9.20

(−11.26 ; −7.15)

−2.71

(−6.55 ; 1.13)

Receiving regular HIV care:

     

 HIV-negative or unaware

428 (52.8)

Ref

-

Ref

-

 HIV+; receives regular HIV care

125 (15.4)

−0.87

(−3.41 ; 1.67)

1.46

(−3.05 ; 5.98)

 HIV+; does not receive regular HIV care

258 (31.8)

−13.77

(−15.95 ; −11.59)

−4.32

(−8.36 ; −0.28)

Tuberculosis history awareness:

     

 No (or don’t know)

757 (93.3)

Ref

-

Ref

-

 Yes

54 (6.7)

−7.46

(−11.15 ; −3.76)

−3.32

(−6.43 ; −0.22)

Hepatitis C history awareness:

     

 No

126 (15.5)

Ref

-

N/A

-

 Yes

685 (84.5)

−10.13

(−13.02 ; −7.23)

  

Treatment of Hepatitis C:

     

 Never diagnosed with HCV

126 (15.5)

Ref

-

Ref

-

 HCV+, never been offered treatment

591 (72.9)

−11.09

(−14.00 ; −8.17)

−4.56

(−7.62 ; −1.50)

 HCV+, was offered treatment, but did not receive it

50 (6.2)

−7.45

(−12.58 ; −2.32)

−7.37

(−12.75 ; −1.99)

 HCV+, was offered treatment and received it

44 (5.4)

−0.27

(−4.53 ; 3.98)

−2.02

(−6.80 ; 2.76)

Hepatitis B history awareness:

     

 No

401 (49.4)

Ref

-

Ref

-

 Yes

410 (50.6)

−9.31

(−11.29 ; −7.34)

−0.05

(−2.36 ; 2.25)

Ever vaccinated against Hepatitis B:

     

 No (or don’t know)

525 (64.7)

Ref

-

Ref

-

 Yes (at least one dose)

286 (35.3)

7.29

(5.07 ; 9.50)

1.63

(−0.74 ;4.00)

VI. CONTACT WITH TREATMENT SERVICES AND PRISON

History of incarceration:

     

 No

537 (66.2)

Ref

-

Ref

-

 Yes

274 (33.8)

−2.41

(−4.64 ; −0.18)

−1.49

(−3.40 ; 0.42)

Having basic medical insurance:

     

 No

156 (19.3)

Ref

-

Ref

-

 Yes

654 (80.7)

2.39

(−0.40 ; 5.17)

1.46

(−1.06 ; 3.98)

Receiving any healthcare services in the last 12 months:

     

 Received

546 (67.3)

Ref

-

Ref

-

 Not received

265 (32.7)

−3.00

(−5.32 ; −0.68)

−1.46

(−3.56 ; 0.64)

Ever received drug abuse treatment:

     

 No

229 (28.2)

Ref

-

N/A

-

 Yes

582 (71.8)

−5.79

(−8.15 ; −3.43)

  

Receiving detoxification services in the last 6 months:

     

 Did not need detox services

646 (79.7)

Ref

-

Ref

-

 Needed, but did not receive detox

99 (12.2)

−10.74

(−14.12 ; −7.35)

−5.39

(−9.00 ; −1.78)

 Needed and received detox

66 (8.1)

−4.00

(−8.04 ; 0.04)

−4.82

(−7.96 ; −1.67)

Ever had difficulties obtaining drug abuse treatment:

     

 Never received treatment (or don’t know)

233 (28.7)

Ref

-

Ref

-

 Had no difficulties

482 (59.4)

−4.44

(−6.89 ; −1.99)

1.26

(−0.93 ; 3.45)

 Had difficulties

96 (11.8)

−10.56

(−13.92 ; −7.20)

−0.74

(−4.14 ; 2.66)

Had difficulties obtaining medical care because of drug use:

     

 No (or don’t know)

764 (94.2)

Ref

-

Ref

-

 Yes

47 (5.8)

−5.10

(−9.48 ; −0.73)

−4.22

(−8.21 ; −0.22)

VII. STIGMA, DISCLOSURE AND POLICE HARASSMENT

Ever experienced police confiscate syringes:

     

 No

599 (73.9)

Ref

-

Ref

-

 Yes

212 (26.1)

−6.00

(−8.41 ; −3.59)

−0.48

(−3.02 ; 2.06)

PWID status disclosure to family/friends:f

     

 Rather disclosed

420 (51.8)

Ref

-

Ref

-

 Rather did not disclose

391 (48.2)

−7.06

(−9.10 ; −5.01)

−0.65

(−2.78 ; 1.48)

PWID status disclosure to a healthcare provider:g

     

 Rather disclosed

278 (34.3)

Ref

-

Ref

-

 Rather did not disclose

533 (65.7)

3.83

(1.67 ; 5.99)

−0.16

(−2.51 ; 2.19)

Internalized PWID stigma:h

     

 Low

417 (51.4)

Ref

-

Ref

-

 High

394 (48.6)

−9.14

(−11.15 ; −7.13)

−3.68

(−5.92 ; −1.44)

PWID stigma consciousness:h

     

 Low

343(42.3)

Ref

-

Ref

-

 High

468 (57.7)

−1.68

(−3.81 ; 0.45)

1.52

(−0.52 ; 3.56)

  1. 95 % CI 95 % confidence interval, HRQoL Health-related quality of life, OLS Ordinary Least Squares, PWID people who inject drugs, Ref Reference Category, VAS Visual Analogue Scale
  2. aDependent Variable is EuroQoL 5D VAS measure of the HRQoL
  3. bNumbers may not sum up to total due to missing values, and % may not sum up to 100 due to rounding
  4. cThe adjusted R2 = 0.37. Four variables (Condom use during the last sexual intercourse, HIV status awareness, Hepatitis C awareness, Ever received drug abuse treatment) were not included into the multivariate regression, because of complete collinearity with other variables in the model
  5. dMarried = legally married or living as married; Not married = widowed, divorced or never married
  6. eThe following classes of drugs are included: opiates, amphetamines, and cocaine
  7. fBased on five questions, each measured on 5-point Likert scale. Individual items scores were summed and dichotomized by median
  8. gBased on one question measured on 5-point Likert scale, and dichotomized by median
  9. hBoth internalized stigma scale and stigma consciousness scale are six items questionnaires measured on the 5-point Likert scale. Individual items scores were summed and dichotomized by median
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BMC Medical Research Methodology

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